WO 91/08272 describes the use of complex ligands in ferroelectric liquid-crystal (FLC) mixtures or in alignment layers of liquid-crystal displays. These substances can be used to modify the alignment or switching behavior of the FLC mixtures to increase the contrast and brightness in the displays and to suppress the formation of ghost images.
However, it has been found in the course of time that complex ligands, in particular those containing nitrogen, decompose on exposure to light (UV light) and heat. The decomposition products are distinguished by a yellow color. If the nitrogen-containing complex ligands are dissolved in liquid crystals, the low stability of the complex ligands finally results in a yellow coloration of the liquid-crystal mixture. If the decomposition of the complex ligand is well advanced, the positive effect of the ligands can in the end even be lost.